Field of the Invention
The present invention relates to a titanium-copper alloy having a plating layer. The present invention particularly relates to titanium-copper foil suitable as a conductive spring material for autofocus camera modules (AFM).
Description of the Related Art
An electronic component called an autofocus camera module (AFM) is used in the camera lens part of a mobile phone. With respect to the autofocus function of the camera of a mobile phone, the lens is moved in a fixed direction by the spring force of a material used in AFM, while it is moved in the direction opposite to the direction in which the spring force of the material works by the electromagnetic force generated by passing current through a coil wound on the surroundings. The camera lens is driven by such a mechanism to exhibit autofocus function (for example, Japanese Patent Laid-Open Nos. 2004-280031 and 2009-115895).
Therefore, the copper alloy foil used in AFM needs strength that can endure the material deformation by the electromagnetic force. If the strength is low, the material cannot endure the displacement by the electromagnetic force, producing permanent deformation (permanent set). If the permanent set is produced, the lens cannot move to a desired position and autofocus function is not exhibited when a certain current is passed.
Cu—Ni—Sn-based copper alloy foil having a foil thickness of 0.1 mm or less and a 0.2% yield strength of 1100 MPa or more has been used for the spring material for AFM. However, by the cost reduction requirement in recent years, titanium-copper foil having a relatively lower material cost than the Cu—Ni—Sn-based copper alloy has come to be used, and the demand is increasing.
Under such a background, various titanium-copper alloys suitable as a spring material for AFM have been proposed. For example, in order to improve the 0.2% yield strength and permanent set resistance of titanium-copper foil, Japanese Patent Laid-Open No. 2014-80670 proposes titanium-copper foil containing 1.5 to 5.0% by mass of Ti with the balance consisting of copper and unavoidable impurities, having a 0.2% yield strength in the direction parallel to rolling direction of 1100 MPa or more, and satisfying the relation of I(220)/I(311) □15, where I(220) and I(311) represent the integrated intensity of a (220) plane and a (311) plane, respectively, which are measured using the X-ray diffraction on the rolling surface. Further, for the purpose of improving permanent set resistance, Japanese Patent Laid-Open No. 2014-37613 proposes titanium-copper foil containing 1.5 to 5.0% by mass of Ti with the balance consisting of copper and unavoidable impurities, having a 0.2% yield strength in the direction parallel to the rolling direction of 1100 MPa or more, and having an arithmetic average roughness (Ra) in the direction orthogonal to the rolling direction of 0.1 μm or less.
On the other hand, a method involving subjecting titanium-copper foil to shape-processing by etching has been employed in the process of producing a spring material for AFM from titanium-copper foil. The resulting spring material is joined to a coil through solder. However, the titanium-copper foil for AFM have been developed mainly for improving strength and permanent set resistance without consideration of adhesion with solder. According to the investigation results by the present inventor, since the adhesion strength of a joined part between solder and titanium-copper foil is low, it is also an important object to improve the adhesion strength of the joined part to increase the reliability of the joined part. Further, when application to AFM is taken into consideration, it is desirable that titanium-copper foil be excellent not only in adhesion strength with solder but also in etching properties.
In view of the above circumstances, an object of the present invention is to provide a titanium-copper alloy which can increase the adhesion strength with solder. Preferably, an object of the present invention is to provide a titanium-copper alloy having not only high adhesion strength with solder but also excellent etching properties.